Electrical fuses and electrical antifuses are used in the semiconductor industry to implement array redundancy, field programmable arrays, analog component trimming circuits, and chip identification circuits. Once programmed, the programmed state of an electrical fuse or an electrical antifuse does not revert to the original state on its own, that is, the programmed state of the fuse is not reversible. For this reason, electrical fuses and electrical antifuses are called One-Time-Programmable (OTP) memory elements.
Programming or lack of programming constitutes one bit of stored information in fuses or antifuses. The difference between fuses and antifuses is the way the resistance of the memory element is changed during the programming process. Semiconductor fuses have a low initial resistance state that may be changed to a higher resistance state through programming, i.e., through electrical bias conditions applied to the fuse. In contrast, semiconductor antifuses have a high initial resistance state that may be changed to a low resistance state through programming.
One type of electrical antifuse operates by breakdown of a dielectric layer upon application of sufficient electric field across two conductors. In an intact, or unprogrammed, antifuse, the integrity of the dielectric layer is preserved, thereby maintaining a high resistance state of the electrical antifuse. To program the electrical antifuse, a high electrical field is applied across the dielectric layer to induce a rupture, thereby causing reduction of resistance across the two electrodes of the electrical antifuse located on opposite sides of the dielectric layer. By detecting the resistance across the dielectric layer, the state of the antifuse may be determined. The resistance value across the two electrodes of the electrical antifuse encodes the “on” or “off” state of the electrical antifuse.
A typical electrical antifuse employs a gate dielectric for the dielectric layer between the two electrodes. The resistance across the two electrodes of an electrical antifuse before programming, or “breakdown,” is typically greater than 1 GΩ. The resistance across the two electrodes of an electrical antifuse after programming, that is, after the breakdown of the dielectric layer between the two electrodes is induced, is typically less than 1 MΩ. A sensing circuit is provided to allow decoding of the information stored in the electrical antifuse. Typically, an electrostatic discharge (ESD) protection circuit is also provided to prevent accidental programming and to enhance the reliability of the electrical antifuse thereby.
One of the challenges in implementing electrical antifuse devices is the high electrical field required to induce breakdown of a dielectric layer between two conductive electrodes. Since the thickness of a silicon oxide based gate dielectric is greater than 1 nm due to limitations on tunneling current, any electrical antifuse employing the gate dielectric as the dielectric layer between two electrodes needs a voltage supply that may generate high enough electrical field to induce dielectric breakdown across the gate dielectric. For this reason, electrical antifuses employing a silicon oxide based gate dielectric typically require several volts, and at least a few volts to induce dielectric breakdown for programming.
Constant scaling of semiconductor devices and development of low power applications have reduced power supply voltage for semiconductor chips. Semiconductor chips having a power supply voltage less than 2.0 volts are routinely manufactured in the semiconductor industry. Generation of an internal high voltage supply circuit takes up space in a semiconductor chip, as well as consuming power. At the same time, programmable memories are needed to encode information in semiconductor chips.
In view of the above, there exists a need for an electrical antifuse structure that may be programmed at a lower power supply voltage in a reliable manner, and methods of manufacturing the same.